The subject-matter of the present invention is novel polymerizable compositions for the manufacture of optical lenses with a high refractive index and a high Abbe number and the optical lenses, in particular ophthalmic lenses, obtained from these compositions.
The term xe2x80x9coptical lens with a high refractive indexxe2x80x9d means an optical lens with a refractive index of greater than or equal to 1.55 and preferably greater than 1.57.
Novel polymerizable compositions according to the invention are preferably of use in the manufacture of spectacle glasses.
An ophthalmic lens with a high refractive index must have all the following characteristics:
a high transmission (transmission generally of greater than 85% and preferably of greater than or equal to 90%), with an absence of or optionally a very low light scattering,
a high Abbe number of greater than or equal to 30 and preferably of greater than or equal to 35, in order to avoid chromatic aberrations,
a low yellowing index and an absence of yellowing over time,
good impact strength (in particular according to the CEN and FDA standards),
good suitability for various treatments (shock-proof primer, anti-glare or hard coating deposition, and the like) and in particular good suitability for colouring,
a glass transition temperature value preferably of greater than or equal to 80xc2x0 C. and better still of greater than 90xc2x0 C., preferably of between 90 and 110xc2x0 C.
In addition, the polymerizable compositions must also be easy to process industrially.
In particular, it is desirable for the polymerizable compositions to be able to be quickly polymerized, in particular by photopolymerization.
Patent Document WO 96/38486 discloses polymerizable compositions for the manufacture of optical lenses with a high index and a high Abbe number comprising 20 to 60% by weight of an acrylate or methacrylate monomer derived from a polycyclic olefin, in particular an acrylate or methacrylate derivative of tricyclodecane, 15 to 60% by weight of a di- or polythiol, 5 to 50% by weight of a divinyl or polyvinyl monomer, the vinyl groups of which do not form a (meth)acrylic group, and 0 to 20% by weight of a polymerizable comonomer which can be chosen from methacrylates, acrylates, thiomethacrylates, thioacrylates, vinyls, vinyl ethers, allyls, epoxides and the like.
Although it is indicated that the polymerizable compositions of this document can be polymerized thermally and/or by UV irradiation, all the implementational examples report a thermal curing, the duration of which is particularly lengthy (8 hours).
Patent Document WO 97/44372 discloses a polymerizable composition for the manufacture of ophthalmic lenses which comprises 2.5 to 100% of a divinyl ester cyclic monomer, 5 to 30% by weight of a di- or polythiol monomer and, optionally, 1 to 40% by weight of a thiodiacrylate or -dimethacrylate monomer.
A subject-matter of the present invention is therefore a composition comprising polymerizable monomers for the manufacture of ophthalmic lenses with a high refractive index and a high Abbe number which is easily polymerizable, in particular which is easily photopolymerizable.
The composition comprising polymerizable monomers according to the invention comprises:
(A) at least one polythio(meth)acrylate monomer;
(B) at least one monomer with a high Abbe number comprising at least two polymerizable groups, preferably two to four polymerizable groups, and at least one bridged cyclic constituent unit, the bridged cyclic constituent unit or units not being bonded directly to an oxygen atom;
(C) at least one polythiol monomer; and, optionally,
(D) at least one other monomer which is copolymerizable with the monomers (A), (B) and (C), the composition being devoid of any other monomer comprising one or more vinyl functional groups, other than (meth)acrylic and thio(meth)acrylic functional groups, which is different from the monomers (B).
By definition, a thio(meth)acrylate monomer is a monomer comprising the 
group, R5 having the meaning which appears hereinbelow.
The monomer (A) is preferably a dithio(meth)acrylate.
The monomer (A) is, preferably again, an aliphatic monomer.
A first class of polythio(meth)acrylate monomers suitable for the compositions according to the invention corresponds to the formula: 
in which:
R4 represents a linear or branched, monovalent or polyvalent, aliphatic hydrocarbonaceous radical or a monovalent or polyvalent, aromatic or heterocyclic group bonded directly to the sulphur atom of the thio(meth)acrylate group or groups by a nucleus or via a linear alkyl chain, it being possible for the R4 radical to comprise, in its chain, one or more groups chosen from xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or 
R5 represents hydrogen or xe2x80x94CH3; and
n2 is an integer from 1 to 6, preferably from 1 to 3.
Mention may be made, among monovalent R4 radicals, of linear or branched C1 to C5 alkyl radicals or radicals of formula: 
in which:
R6 and R7 are, independently of one another, H or a linear or branched C1-C5 alkyl radical;
R8 is a linear or branched C1-C5 alkyl radical, a C7-C10 aralkyl radical or a C6-C12 aryl radical which is optionally substituted, in particular by alkyl and/or halogen groups; and
n3 is an integer from 1 to 4.
Mention may be made, among preferred monovalent R4 radicals, of:
C2H5SCH2CH2xe2x80x94;

Monomers of formula (I) for which n2=1 and which are as defined above are disclosed, inter alia, in Patents U.S. Pat. No. 4,606,864, JP-63316766 and EP-A-0,384,725.
Mention may be made, among divalent R4 radicals coming within the context of the monomers of formula (I), of linear or branched C2 to C10 alkylene radicals which can comprise, in their chain, one or more xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or 
groups, alkylidene radicals of formula 
in which R9 and R10 are C1-C5 alkyl radicals, radicals of formula: 
in which R11 and R12 are linear or branched C1-C5 alkylene groups which can comprise one or more xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or 
groups in their chains, Xxe2x80x3 is chosen from C1-C5 alkyl radicals and halogens, and n4 is an integer from 0 to 4, and radicals of formula: 
in which R13 and R14 are linear or branched C1 to C5 alkylene radicals which can comprise, in their chain, one or more xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or 
groups and t and s are equal to 0 or 1.
Mention may be made, among preferred divalent R4 radicals, of the following radicals:
"Parenopenst"CH2"Parenclosest"qxe2x80x2, where qxe2x80x2 is an integer from 1 to 8;
"Parenopenst"CH2CH2X"Parenclosest"uCH2CH2xe2x80x94, where X is xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94 and u is an integer from 1 to 4;
"Parenopenst"CH2"Parenclosest"uxe2x80x2"Brketopenst"S(CH2)vxe2x80x2"Brketclosest"zxe2x80x2"Parenopenst"CH2"Parenclosest"wxe2x80x2, where zxe2x80x2 is equal to 0 or 1 and uxe2x80x2, vxe2x80x2 and wxe2x80x2 are integers from 2 to 6; 
where uxe2x80x3 and vxe2x80x3 are integers from 1 to 4, 
Particularly preferred divalent R4 radicals are: 
Divalent monomers of formula (I) are disclosed, inter alia, in Patents EP-A-273,661, EP-A-273,710 and EP-A-384,725.
Mention may be made, among trivalent R4 radicals of the monomers of formula (I), of C3 to C10 alkyltriyl radicals which can comprise, in their chain, one or more xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or 
groups, trivalent alkylaryl radicals, the alkyl chains of which comprise one or more xe2x80x94Sxe2x80x94 or xe2x80x94Oxe2x80x94 groups, and trivalent aryl groups.
Mention may be made, among trivalent R4 radicals or R4 radicals with a higher valency, of: 
and the like.
Mention may be made, among monomers of formula (I) recommended in the present invention, of: 
S-2-acryloyloxyethyl thio(meth)acrylate, 
S-2-methacryloyloxyethyl thio(meth)acrylate, 
1,2-bis[(meth)acryloylthio]ethane, 
1,2-bis[(meth)acryloylthio]propane, 
1,3-bis[(meth)acryloylthio]propane, 
1,4-bis[(meth)acryloylthio]butane, 
bis[2-(meth)acryloylthioethyl]ether, 
bis[2-(meth)acryloylthioethyl]sulphide, 
bis[2-(meth)acryloylthioethoxy]methane, 
bis[2 -(meth)acryloylthioethylthio]methane, 
1,2-bis[2-(meth)acryloylthioethoxy]ethane, 
1,2-bis[2-(meth)acryloylthioethylthio]ethane, 
bis[2-(2-(meth)acryloylthioethoxy)ethyl]ether, 
bis[2-(2-(meth)acryloylthioethylthio)ethyl]sulphide, 
1,4-bis[(meth)acryloylthio]benzene, 
1,4-bis[(meth)acryloylthiomethyl]benzene, 
benzylthioethyl thio(meth)acrylate, 
1,4-bis[(meth)acryloylthio]-2,3-dimethylthiobutane, 
1,2,3-tris[(meth)acryloylthioethylthio]propane, and 
bis[(meth)acryloylthiophenyl]sulphide,
where R5 represents a hydrogen atom or a methyl group.
Another class of thio(meth)acrylic monomers suitable in the compositions comprising monomers according to the invention corresponds to the formula: 
in which R5 represents H or CH3, R15 represents an optionally branched C2-C12 alkylene group, a C3-C12 cycloalkylene group, a C6-C14 arylene group or a C7-C26 alkarylene group, it being possible for the carbonaceous chain of the R15 group to be interrupted by one or more ether or thioether groups, and n5 is an integer from 1 to 6.
Such monomers are disclosed in U.S. Pat. No. 5,384,379.
A recommended polythiomethacrylate monomer is bis(2-methacryloylthioethyl)sulphide (BMTES).
The polythiomethacrylate monomer or monomers generally constitute from 10 to 60% by weight, preferably 25 to 60% by weight, with respect to the total weight of polymerizable monomers present in the composition.
The monomers (B) with a high Abbe number suitable for the compositions of the invention are monomers comprising at least two, preferably two to four, polymerizable groups and at least one bridged cyclic constituent unit, the bridged cyclic constituent unit or units not being bonded directly to an oxygen atom.
The bridged cyclic constituent units are preferably chosen from norbornenyl and dicyclopentenyl radicals and their divalent hydrogenated derivatives.
The polymerizable groups are preferably (meth)acrylic or thio(meth)acrylic groups or bridged cyclic groups comprising an intracyclic ethylenic double bond or a linear or branched aliphatic residue comprising an ethylenic unsaturation, preferably a vinyl or ethylidene group bonded directly to a carbon of the ring.
The bridged cyclic polymerizable groups can be chosen from the groups of formulae: 
where n is an integer from 0 to 5 inclusive, k is an integer from 0 to 3 inclusive and j is an integer from 0 to 10 inclusive, and 
where n is an integer from 0 to 5 inclusive, kxe2x80x2 is an integer from 0 to 2 inclusive and jxe2x80x2 is an integer from 0 to 10 inclusive, Q represents a xe2x80x94C(Rxe2x80x2)2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NRxe2x80x2xe2x80x94 or xe2x80x94SO2xe2x80x94 group, with Rxe2x80x2 denoting H or a C1-C3 alkyl radical, preferably a hydrogen atom or xe2x80x94CH3, and R is a hydrogen atom or a C1-C3 alkyl radical, preferably xe2x80x94CH3.
Mention may be made, among preferred groups above, of groups of formulae: 
in which the R radicals represent, independently of one another, a hydrogen atom or a C1-C3 alkyl group, for example methyl, preferably a hydrogen atom, Q is a divalent radical chosen from xe2x80x94C(Rxe2x80x2)2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94 or xe2x80x94NRxe2x80x2xe2x80x94, where Rxe2x80x2 is a hydrogen atom or a C1-C3 alkyl radical, preferably a methyl radical, Q preferably being a xe2x80x94CH2xe2x80x94 radical, n=0 to 5 and m=0 to 8.
It is obvious that, when the functional groups of the monomer (B) are thio(meth)acrylate groups, the monomers (A) and (B) present in the composition are different monomers.
More preferably, a monomer with a high Abbe number is chosen, the refractive index of which is at least 1.56.
A first class of monomers (B) with a high Abbe number is composed of monomers comprising polymerizable (meth)acrylic or thio(meth)acrylic end groups comprising, in their chains, a bridged cyclic constituent unit as defined above.
Among these monomers with a high Abbe number, recommended monomers correspond to the formula: 
in which Q and R5 are defined as above, X represents xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94, a=1-3, b=1-3, g and gxe2x80x2 vary from 0 to 6, and G and Gxe2x80x2 are divalent groups chosen from one or more of the following groups: 
in which r=1-4.
Preferred compounds of this class are di(meth)acryloyls of hydroxymethyltricyclodecane and dithio(meth)acryloyls of hydroxymethyltricyclodecane.
A particularly recommended compound is the compound of formula: 
Compounds corresponding to the above formula (III) are disclosed in Patent Document WO 96/38486.
Another class of monomers (B) which is recommended are monomers comprising polymerizable bridged cyclic end groups, in particular norbornenyl and dicyclopentenyl groups.
More particularly, compounds of this class correspond to the general formula:
Z"Parenopenst"A)naxe2x80x83xe2x80x83(IV)
in which na is an integer from 2 to 4 and A is a radical chosen from radicals of formulae: 
in which Q represents xe2x80x94C(Rxe2x80x2)2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94 and xe2x80x94NRxe2x80x2xe2x80x94, where Rxe2x80x2 represents H or a C1-C3 alkyl radical, R represents hydrogen or a C1-C3 alkyl radical, preferably CH3, n=0-5 and m=0-8, and
(I) when na=2, Z represents a divalent radical of a formula: 
in which formulae X represents xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94, G1 and Gxe2x80x21 are "Parenopenst"Cn.H2n.O"Parenclosest"mxe2x80x2 groups, with nxe2x80x2=1 to 5, preferably nxe2x80x2=2, and mxe2x80x2 varies from 0 to 10, or a C1-C5 alkylene group, Z1 is chosen from divalent radicals of formulae: 
in which formulae Q is defined as above, B1 represents xe2x80x94C(R2)2xe2x80x94 or xe2x80x94Sxe2x80x94, R2 is a C1-C3 alkyl radical, preferably xe2x80x94CH3, x1=0 or 1, Y1 represents, independently of one another, Br, Cl or H, y1 is an integer from 0 to 4, the Rb groups denote, independently of one another, a "Parenopenst"CH2"Parenclosest"q group, q is an integer from 1 to 4, preferably equal to 1 or 2, and p is an integer from 0 to 4, preferably from 0 to 2; and
Z2 is a divalent radical chosen from radicals of formulae: 
xe2x80x94Rb"Brketopenst"Sxe2x80x94Rb"Brketclosest"pxe2x80x94Rb"Brketopenst"SRb"Brketclosest"pZ3"Brketopenst"RbS"Brketclosest"pRbxe2x80x94, where Q, Rb and p are defined as above and Z3 is a divalent radical chosen from: 
where Q and x1 are defined as above;
(II) when na=3, Z represents a trivalent radical chosen from: 
where Rb and p are defined as above and Rc represents H or a C1-C3 alkyl group, preferably xe2x80x94CH3; and
(III) when na=4, Z represents a tetravalent radical chosen from the following radicals:
C"Brketopenst"R3"Brketclosest"4, where R3 is a C1-C5 alkylene radical or a "Brketopenst"SRb"Brketclosest"pSxe2x80x94 radical where Rb and p are defined as above.
Preferred monomers of this class correspond to the formula: 
where R is H or CH3, X is xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94, B is xe2x80x94Sxe2x80x94 or 
nxe2x80x2 and nxe2x80x3=1 to 5 and mxe2x80x2 and mxe2x80x3 vary from 0 to 10. Preferably, 3xe2x89xa6mxe2x80x2+mxe2x80x3xe2x89xa65 and nxe2x80x2 and nxe2x80x3=2.
A monomer of this type which is particularly recommended is the monomer of formula: 
Bisphenol A 2-ethoxylate dinorbornenecarboxylate.
Polymerizable monomers of this type are disclosed, inter alia, in Patent Document WO 88/02902.
Mention may also be made, among preferred monomers comprising end polycycloalkenyl groups, of monomers of formula: 
where R=H or CH3, Rb is as defined above, preferably a propylene radical, pxe2x80x2 is an integer from 1 to 3, preferably equal to 2, and pxe2x80x3 is an integer equal to 0 or 1.
A recommended monomer of formula (VIII) is the monomer of formula: 
(MESDTMN) or mercaptoethyl sulphide dithiomethnorbornenecarboxylate.
Mention may be made, among monomers of formula (VI) above, of monomers in which Z2 represents the following groups: 
Such monomers, and the process for their preparation, are disclosed in Patent Document JP-81 51360.
Mention may be made, among recommended trivalent monomer constituents comprising end polycycloalkenyl groups, of monomers of formulae: 
Polymerizable monomers (B) represent 5 to 50%, preferably 10 to 40%, by weight with respect to the total weight of polymerizable monomers present in the composition.
The third essential constituent of the compositions according to the invention is a polymerizable polythiol monomer (C).
Polythiol monomers which are suitable for the compositions according to the present invention are well known in the art and can be represented by the formula R1(SH)n1 in which n1 is an integer of 2 or more, preferably from 2 to 5, and R1 is an aliphatic, aromatic or heterocyclic radical.
The polythiol compound is preferably a dithiol, trithiol or tetrathiol compound, in particular a polythiol with a high Abbe number.
These polythiol compounds are well known in the art and are disclosed, inter alia, in Document EP 394,495.
Mention may be made, among dithiols of use in the present invention, of 9,10-anthracenedimethanethiol, 1,11-undecanedithiol, 4-ethylbenzene-1,3-dithiol, 1,2-ethanedithiol, 1,8-octanedithiol, 1,18-octadecanedithiol, 2,5-dichlorobenzene-1,3-dithiol, 1,3-(4-chlorophenyl)propane-2,2-dithiol, 1,1-cyclohexanedithiol, 1,2-cyclohexanedithiol, 1,4-cyclohexanedithiol, 1,1-cycloheptanedithiol, 1,1-cyclopentanedithiol, 4,8-dithiaundecane-1,11-dithiol, dithiopentaerythritol, dithiothreitol, 1,3-diphenylpropane-2,2-dithiol, 1,3-dihydroxy-2-propyl 2xe2x80x2,3xe2x80x2-dimercaptopropyl ether, 2,3-dihydroxypropyl 2xe2x80x2,3xe2x80x2-dimercaptopropyl ether, 2,6-dimethyloctane-2,6-dithiol, 2,6-dimethyloctane-3,7-dithiol, 2,4-dimethylbenzene-1,3-dithiol, 4,5-dimethylbenzene-1,3-dithiol, 3,3-dimethylbutane-2,2-dithiol, 2,2-dimethylpropane-1,3-dithiol, 1,3-di(4-methoxyphenyl)propane-2,2-dithiol, 3,4-dimethoxybutane-1,2-dithiol, 10,11-dimercaptoundecanoic acid, 6,8-dimercaptooctanoic acid, 2,5-dimercapto-1,3,4-thiadiazole, 2,2xe2x80x2-dimercaptobiphenyl, 4,4xe2x80x2-dimercaptobiphenyl, 4,4xe2x80x2-dimercaptobibenzyl, 3,4-dimercaptobutanol, 3,4-dimercaptobutyl acetate, 2,3-dimercapto-1-propanol, 1,2-dimercapto-1,3-butanediol, 2,3-di-mercaptopropionic acid, 1,2-dimercaptopropyl methyl ether, 2,3-dimercaptopropyl 2xe2x80x2,3xe2x80x2-dimethoxypropyl ether, 3,4-thiophenedithiol, 1,10-decanedithiol, 1,12-dodecanedithiol, 3,5,5-trimethylhexane-1,1-dithiol, 2,5-toluenedithiol, 3,4-toluenedithiol, 1,4-naphthalenedithiol, 1,5-naphthalenedithiol, 2,6-naphthalenedithiol, 1,9-nonanedithiol, norbornene-2,3-dithiol, bis(2-mercaptoisopropyl)ether, bis(11-mercaptoundecyl)sulphide, bis(2-mercaptoethyl)ether, bis(2-mercaptoethyl)sulphide, bis(18-mercaptooctadecyl)sulphide, bis(8-mercaptooctyl)sulphide, bis(12-mercaptodecyl)sulphide, bis(9-mercaptononyl)sulphide, bis(4-mercaptobutyl)sulphide, bis(3-mercaptopropyl)ether, bis(3-mercaptopropyl)sulphide, bis(6-mercaptohexyl)sulphide, bis(7-mercaptoheptyl)sulphide, bis(5-mercaptopentyl)sulphide, 2,2-bis(mercaptomethyl)acetic acid, 1,1-bis(mercaptomethyl)cyclohexane, bis(mercaptomethyl)durene, phenylmethane-1,1-dithiol, 1,2-butanedithiol, 1,4-butanedithiol, 2,3-butanedithiol, 2,2-butanedithiol, 1,2-propanedithiol, 1,3-propanedithiol, 2,2-propanedithiol, 1,2-hexanedithiol, 1,6-hexanedithiol, 2,5-hexanedithiol, 1,7-heptanedithiol, 2,6-heptanedithiol, 1,5-pentanedithiol, 2,4-pentanedithiol, 3,3-pentanedithiol, 7,8-heptadecanedithiol, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 2-methylcyclohexane-1,1-dithiol, 2-methylbutane-2,3-dithiol, ethylene glycol dithioglycolate or ethylene glycol bis(3-mercaptopropionate). Mention may be made, among trithiols, of 1,2,3-propanetrithiol, 1,2,4-butanetrithiol, trimethylolpropane trithioglycolate, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol trithioglycolate, pentaerythritol tris(3-mercaptopropionate), 1,3,5-benzenetrithiol and 2,4,6-mesitylenetrithiol.
Mention may also be made, among polythiols of use in the compositions of the present invention, of neopentanetetrathiol, 2,2-bis(mercaptomethyl)-1,3-propanedithiol, pentaerythritol tetrakis(3-mercaptopropionate), 1,3,5-benzenetrithiol, 2,4,6-toluenetrithiol, 2,4,6-methylenetrithiol and polythiols corresponding to the formulae: 
(HSCH2CH2COOCH2)3CC2H5 (TMPT), and 4-mercaptomethyl-3,6-dithia-1,8-octanedithiol.
The polythiol monomer (C) generally represents 10 to 60% by weight, preferably 20 to 50% by weight, with respect to the total weight of polymerizable monomers present in the composition.
The compositions according to the invention can also comprise other polymerizable monomers (D), with the exception of monomers comprising vinyl functional groups other than (meth)acrylate or thio(meth)acrylate groups.
Mention may be made, among these other monomers, of monomers or mixtures of monomers of formula: 
in which R5independently represents H or CH3 and m2+n2 has a mean value from 0 to 20 inclusive.
Preferred monomers of formula (IX) are compounds in which R5=CH3 and m2+n2=2.6 (EBADMA), m2+n2=4 (DBADMA) and m2+n2=10 (OBADMA).
The particularly preferred monomer is bisphenol A bis(diethoxymethacrylate) (DBADMA).
These monomers represent from 0 to 60% by weight, preferably 10 to 50% by weight, of polymerizable monomers present in the composition.
The polymerizable compositions according to the invention can also comprise additives conventionally used in polymerizable compositions for the moulding of optical articles, in particular spectacle glasses, in conventional proportions, namely inhibitors, colorants, UV absorbers, fragrances, deodorants, antioxidants and anti-yellowing absorbents.
Mention may be made, as preferred examples of antioxidizing agents, of triphenylphosphine (TPP) and Irganox(copyright) 1010 (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (CG1010).
Fragrances make it possible to mask the odour of the compositions, in particular during surface working operations.
The compositions according to the invention generally comprise polymerization initiators, preferably photoinitiators or mixtures of photoinitiators and of thermal initiators, in a proportion of 0.001 to 5% by weight with respect to the total weight of polymerizable monomers present in the composition.
Mention may in particular be made, among photoinitiators which can be used in the polymerizable compositions according to the invention, of 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO), 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, alkylbenzoyl ethers, the photoinitiator sold by the Company Ciba-Geigy under the name CGI 1700, which is a 25/75 mixture of a compound of formula: 
and of a compound of formula: 
and the photoinitiator CGI 1850 sold by the Company Ciba-Geigy, which is a mixture (50/50) (by weight) of compound A and of Irgacure(copyright) 184 of formula: 
As indicated above, the preferred polymerizable compositions according to the invention are photopolymerizable compositions comprising one or more photoinitiators.
More preferably, the polymerizable compositions according to the invention are photo- and thermo-polymerizable compositions comprising both a polymerization photoinitiator and a polymerization thermal initiator.
Thermal polymerization initiators are compounds which are well known in the art and mention may be made, among them, of peroxides, such as benzoyl peroxide, cyclohexyl peroxydicarbonate, isopropyl peroxydicarbonate and t-butyl peroxy(2-ethylhexanoate).
Monomers of formula (IV) can be synthesized either by a Diels-Alder reaction between a compound comprising two or more (meth)acrylate or thio(meth)acrylate functional groups and a cycloalkene, such as cyclopentadiene or norbornadiene, or by addition of thiol/ene type between a polythiol compound and an ene compound, such as cyclopentadiene, norbornadiene, vinylnorbornene or ethylidenenorbornene.
The polythiol compound and the ene compound are reacted in proportions corresponding substantially to one thiol group of the polythiol compound or compounds per mole of ene compound.
By way of example, the scheme is shown below for the synthesis of monomers with a high Abbe number according to the invention from 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene with a dithiol: 
where W is an aliphatic or aromatic radical.